332 Insect Architecture. 



mouth, but by air-lioles, or spiracles, eighteen in number, 

 situated along the sides, in the middle of the rings, as may- 

 be seen in the following figure from Lyonnet. 



These spiracles communicate on each side with tubes, that 

 have been called the wind-pipes (trachece). The spinning 

 apparatus is placed near the mouth, and is connected with 

 the silk-bags, which are long, slender, floating vessels, con- 

 taining a liquid gum. The bags are closed at their lower 

 extremity, become wider towards the middle, and more slen- 

 der towards the head, where they unite to form the spinning- 

 tube, or spinneret. The bags being in most cases longer 

 than the body of the caterpillar, necessarily lie in a convolu- 

 ted state, like the intestines of quadrupeds. The capacity, 

 or rather the length, of the silk -bags is in proportion to the 

 quantity of silk required for spinning ; the Cossus ligniperda, 

 for example, from living in the wood of trees, spins little, 



Caterpillar of the Goat Moth (Cossus ligniperda}. 



having a bag only one-fourth the length of that of the silk- 

 worm, though the caterpillar is at least twice the dimensions 

 of the latter. The following figure, taken from the admirable 

 treatise of Lyonnet on the anatomy of the Cossus, will render 

 these several organs more easily understood than any descrip- 

 tion. 



The spinneret itself was supposed by Reaumur to have 

 two outlets for the silk ; but Lyonnet, upon minute dissection, 

 found that the two tubes united into one before their termi- 

 nation ; and he also assured himself that it was composed 

 of alternate slips of horny and membranaceous substance, 

 the one for pressing the thread into a small diameter, and the 

 other for enlarging it at the insect's pleasure. It is cut at 

 the end somewhat like a writing-pen, though with less of a 

 slope, and is admirably fitted for being applied to objects to 



